In a first typical image forming apparatus including a double-sided print function, high-speed printing is performed as follows. After an image is transferred onto a sheet (for example, a paper sheet) by a print engine, the sheet is conveyed and reversed to return to the print engine, while a succeeding sheet is then conveyed to the print engine to have an image transferred thereonto. In typical high-speed printing image forming apparatuses, a video memory of the print engine has a storage capacity that is capable of storing the data corresponding to a certain number of pages.
In a second typical image forming apparatus including an electronic sorting function used during the printing of a plurality of copies, a video memory of a print engine has a storage capacity that is capable of storing the data corresponding to a certain number of pages. In an example operation, image data on a subsequent page is to be transferred from a printing control unit to the video memory for an engine controller. When the image data on the page that has already been transferred at the previous time and remains on the video memory, the transfer of the image data on the subsequent page is omitted, and as a result, the image data on the page on the video memory is reused, thereby reducing the processing time.